The art of packaging ICs has continued to evolve and today represents a tremendous engineering challenge as ICs become smaller and more transistor dense. The packages encase many varieties of ICs, such as microprocessors, application specific ICs, cache and system memory, and range from packaging a single ICs to multiple ICs. No matter which type of package is used, the considerations for packaging are all generally the same. For example, packages are desired that are relatively inexpensive, are mechanically stable, are properly sized and can reliably distribute electric signals between various circuits and components while removing unwanted heat and offering protection in hostile environments. As expected, a trade-off exists between simultaneously being able to optimize each of the above considerations.
In conventional BOC package configurations, an IC in the form of a die is secured to a printed circuit board (PCB) by means of a two-sided tape that is sandwiched between the die and PCB. After curing, the die is electrically connected to the PCB via wire bonding and over-molded with an epoxy molding compound to form a complete package. The over-molding is typically performed in a molding cavity under high temperature and pressure conditions, such as 180° C. and 1000 psi, where the epoxy molding compound is forced to fill crevices in and around the wire bonds, the die and the PCB. During cooling, however, tremendous thermal mismatch occurs between all the foregoing mentioned structures which mechanically stresses the package. As a result, silica filler in the epoxy molding compound (typically 80-90% by weight) often impinges upon the die and the PCB and frequently mechanically and/or electrically compromises the package.
Thereafter, manufacturers typically perform package testing. Some of the tests are performed according to convention, such as the JEDEC standard tests, where assessment of a package's moisture sensitivity, thermal shock and temperature cycle, to name a few, is undertaken. The tape, however, is notoriously known for becoming de-laminated from one or both of the die and the PCB during such tests. Not only does de-lamination result in an inferior package, it also severely limits a manufacturer's ability to market its product since many IC packages are marked according to what level of JEDEC test was passed. For example, with level 1 being the best and level 4 being the worst, an IC package marked as a level 3 means it passed the level 3 test but failed the level 2 test. Some manufacturers even consider the tape to be the most limiting factor in all JEDEC testing.
Accordingly, the packaging arts desire an efficaciously formed package having improved thermal properties that are capable of achieving a higher pass rate during testing.